A conventional Q-switch laser control is described hereinafter. A conventional Q-switch laser system obtains pulsed light by controlling a Q-switch and excitation light of a resonator which comprises a high reflecting mirror, the Q-switch, a gain medium, an output mirror, and an excitation light medium.
Incidence of the excitation light into the gain medium generates optical resonation between the high reflecting mirror and the output mirror, thereby oscillating laser. Interposing the Q-switch on the way opens a light path when the Q-switch element is turned on, i.e., the Q-switch is turned into a continuous oscillation mode, so that laser is oscillated. However, when the Q-switch element is turned off, i.e., the Q-switch is turned into a pause time, the light path is closed and the oscillation is halted.
Then turning on the Q-switch, i.e., in the continuous oscillation mode, generates a higher power pulse because a loss of the resonator decreases in a short time. Switching the ON and OFF of the Q-switch thus allows oscillating a pulse laser.
In general, when this Q-switch oscillation is carried out, a peak value of a first pulse of the oscillation is unduly great as shown in FIG. 14. In order to suppress this greater peak value, the light exciting a gain medium is weakened as shown in FIG. 15 just before the first pulse. This is known as a first-pulse suppression method.
Instead of the first-pulse suppression method, in order to suppress the greater peak of the first pulse, the exciting light is continuously emitted to the gain medium. The Q-switch is thus set in the continuous excitation mode for preparing a given pause time before a laser pulse is generated as shown in FIG. 16. This is known as Q-switch laser.
A laser machine employing this Q-switch laser is used for machining a metal or piercing holes on a printed board. During the machining operation, a pulse train at a given frequency is needed and a long pause is taken for transporting a workpiece, so that a pulse oscillation and a pause are alternately repeated.
The foregoing method is a practical and effective method to produce a laser pulse, namely, emit the exciting light continuously to the gain medium for setting the Q-switch in the continuous oscillation mode, and prepare a given pause time before the laser pulse is generated. However, use of a higher frequency sometimes makes a peak value of the first pulse higher than those of the second pulse and onward as shown in FIG. 16.
Due to a thermal lens in an optical component disposed in the oscillator, the peaks of first several pulses stay higher or lower than those of pulses stabilized after a given period of time as shown in FIGS. 17(A) and 17(B).
When the laser machine uses such laser pulses as shown in FIGS. 17(A) and 17(B), a first shot or each one of first several shots measures out of a desirable diameter as shown in FIGS. 18(A) and 18(B).
In order to overcome this inconvenience, emit laser to a dummy target until the pulses are stabilized, then the machining is started. This method however wastes the preparatory time before starting the machining.
The present invention addresses the problems discussed above, and aims to provide a method of controlling laser, and a laser device, both of which produce stable laser-pulse laser and need no useless time in a machining operation.